Self-Assembly of Well-Defined PS-b-PDMS Copolymers in Bluk and in Selective Solvents

MARIO D. NINAGO; ANDRÉS E. CIOLINO; MARCELO A. VILLAR; FERNANDO C. GIACOMELLI; PETR CERNOCH; PETR STEPÁNEK; VANESA SCHMIDT; CRISTIANO GIACOMELLI

Roma, Italia

Congreso; 9th International Conference on Chemical and Process Engineering, IcheaP-9; 2009

AIDIC

One of the most interesting and fascinating properties of well defined block copolymers is their ability to self-assemble into a wide variety of morphologies either in solution (spherical micelles, vesicles, cylinders, etc.) or in bulk (lamellas, bicontinuous gyriods and hexagonally or tetragonally packed cylinders, cubic phases, etc.). They constitute, therefore, a collection of elementary building-blocks for the precise construction of novel materials via bottom-up, atom- and energy-efficient approaches. The shape and size of assembled morphologies are determined by a number of factors, such as the relative block lengths, the chemical nature of the blocks, and the type of solvent employed for the synthesis or the preparation of the solution. The micellization process leads to the formation of ordered structures in which the contact between the insoluble block and the solvent is minimized. The soluble block is then oriented towards the continuous solvent phase and becomes the core of the formed micelle, whereas the insoluble part will be shielded from the solvent in the core of the structure, and therefore protected from the external environment. Depending upon the interactions of the corona chains and the relative compositions of the block copolymers, micelles of various shapes can be formed, most often with spherical or cylindrical morphologies. Stable aggregates with a range of morphologies are obtained under various conditions. In this work we report the synthesis of poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) copolymers through sequential anionic polymerization, and their self-assembly behavior in bulk (thin films) and in solution (nanoparticles) as a function of the macromolecular characteristics (molar weight and relative volume fraction of the monomers). In bulk, well-defined island-type structures with periodic separation and uniform height were obtained in films prepared by spin casting onto silicon wafers, as evidenced by atomic force microscopy (AFM). In solution, micellar core-shell nanoparticles were observed in different media, and the corresponding structure was determined in details by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS).